Originally Posted by LordFoo

If your setup is a standard (Shimano) road double with the recommended BB, your current chainline should be 43.5mm at the spider, 41mm for the inner ring, and 46mm for the outer ring (referenced from http://www.sheldonbrown.com/chainline.html).

In this case, if your rear wheel is the "standard" 42mm chainline, you should be able to get away with using just the inner ring; if you want the outer ring (aesthetic reasons?), you'll need a BB with a shorter spindle and will need to make sure that your chainring isn't so big that it'll hit the chainstay.